Detective Superintendent Steve Wade said thousands of hours of CCTV footage were studied, more than 6,000 mobile phone checks were carried out and a substantial number of internet usage inquiries were made.

It was also a case of significant interest, since it raised concerns among Chinese people about whether it was safe for their children to come to the UK to study.

When Mr Wade held a news conference in London especially for the Chinese media, it is estimated that half a billion people watched the resulting footage.

Mr Wade said there was speculation in the early stages of the inquiry that the murders were racially motivated.

Although he knew that his suspect was of oriental origin - this was never made public during the investigation - the officer did not want to alert the killer or killers.

"Each homicide investigation brings its own unique challenges, but there was an added dimension to this one," said Mr Wade.

"We had the deaths of two young people who came to this country from the other side of the world and their parents were obviously devastated.

"Their parents had some natural scepticism about how police in the UK operate - it was completely outside the realm of their previous experience or knowledge and all communication has been through an interpreter.

"We did everything possible to meet these challenges, keeping them updated about the investigation, taking them through the prosecution process, helping them watch the court proceedings and explaining where necessary.

"I’ve been impressed by their patience, courage and dignity under extremely traumatic circumstances.

"I know that they, in turn, have been overwhelmed by the scale, skill, diligence and professionalism of the investigation which has brought about this conviction."

Mr Wade thanked all those who assisted in the investigation.

"The Chinese community and Victim Support have rallied round the victims’ families, both at their funerals and during the trial," he said.

"I am also extremely grateful to all of those mentioned above, and also to the many witnesses who bravely came to court to give evidence."